The invention relates to the electric coupling of an electrode connection to a current output terminal. The invention applies in particular to electrochemical generators intended for portable equipment, the capacity of which is generally less than 20 Ah, particularly for sealed cylindrical secondary electrochemical generators with spirally wound electrodes. The invention relates in particular to the method for producing this coupling.
An electrochemical generator comprises an electrochemical stack comprising an alternating sequence of positive and negative electrodes framing a separator impregnated with electrolyte. Each electrode most often comprises a metal current conductor support carrying the electrochemically active material on at least one of its surfaces. The electrode is connected electrically to a current output which ensures electrical continuity between the electrode and the external application with which the generator is associated. This current output can be the container of the generator, such as for example the cover, or a current output terminal mounted on the container.
Standard cylindrical generators generally have spiralling of an electrochemical stack forming a cylindrical body. The spiralling then comprises two electrodes with respectively positive and negative polarity framing a separator. There are several ways of electrically coupling an electrode to a current output.
One of these ways is the use of at least one thin conducting strip or thin metal band, one end of which is welded to the end face of the current conductor support of one of the electrodes and the other end is welded to the part of the current output situated inside the container, for example to the internal surface of the cover or to the internal part of a terminal.
Another method consists in bringing a flat current collector into contact with one of the flat ends of the cylindrical body formed by the winding of a portion of the current conductor support of one of the electrodes. In this case the two electrodes have a slight difference in height so that each end of the cylindrical body is formed by the spirally wound portion of the current conductor support of only one of the two electrodes. The flat current collector, in the shape of a disk for example, can itself be provided with at least one thin conducting strip connected to the current output.
In practice, in order to connect an electrode to a current output, for example to a terminal which passes through a cover, the end of the thin strip is positioned, held and fixed on the internal part of the terminal. To carry out this operation it is necessary to create a space for positioning the welding tool. During this operation the cover is in a position approximately perpendicular to its closed position. The generator is then closed using the cover which is folded down. In this embodiment, the positioning of the thin strip vis-à-vis the internal part of the terminal proves awkward. The closing of the cover engenders a complex folding of the connection which is not controlled. During this operation, there is a risk of damaging the fixing of the thin strip to the terminal, or even the thin strip itself.
For example, EP-0 818 842 discloses a cylindrical alkaline electrolyte generator comprising two spirally wound electrodes so that each end of the cylindrical body is formed by the winding of a portion of the conductor support of a single electrode. A perforated flat current collector is welded to the upper end face of the conductor support of one of the electrodes. A collecting plate connected to the flat connector is spot-welded to the internal surface of the cover while the cover is in a position perpendicular to its closed position. The cover is then folded down in order to hermetically seal the casing by means of an insulation gasket. The collecting plate has sufficient length so as to have, once folded, a fairly extensive contact surface with the internal surface of the cover. After closing the generator, a voltage of 24 Volts is applied in a discharge direction between the cover and the bottom of the casing so as to cause the flow of a current of 1 KA for 15 msec. Thus a second welding is carried out between the collecting plate and the internal surface of the cover. The electric coupling thus obtained has better mechanical strength in a vibration test. However the positioning of the collecting plate on the internal surface of the cover when closing the generator proves to be a delicate operation to carry out. Moreover when carrying out the second welding a disconnection of the first weld can occur or melting of the collecting plate if the duration and intensity of the current are not perfectly controlled.